Those have been used for a while. Reliance still makes one:
http://www.google.com/products/catalog? ... F4Q8wIwAw#
I noticed that Walmart is no longer selling this model on-line but may still have a few in their stores or other places.
The advantage with this type of potty is that they fold down to a nice small size for packing and transport. The disadvantage is that the plastic in the legs eventually begins to weaken and eventually gives way or breaks, leaving the pottying person in a literal mess.

(My girlfriend was a victim of this problem.)
If you decide to use it, you can still get the bags with the chemical in them in the sporting goods section of local Walmart stores and other sporting goods stores. But, check those legs very, very well...
every time you take it camping. It would probably be better to go with a Luggable Loo or the shorter Portable Hassock, both of which are sold on-line.